Liquid electrophotographic ink composition

ABSTRACT

A method for coating pigment particles is provided, the method comprising heating a polymer resin in a carrier fluid to dissolve the polymer resin, suspending in the carrier fluid the pigment particles to be coated; and effecting precipitation of the polymer resin from the carrier fluid, such that a coating of the resin is formed on the pigment particles.

BACKGROUND

Electrostatic printing processes typically involve creating an image ona photoconductive surface, applying an ink having charged particles tothe photoconductive surface, such that they selectively bind to theimage, and then transferring the charged particles in the form of theimage to a print substrate.

The photoconductive surface is typically on a cylinder and is oftentermed a photo imaging plate (PIP). The photoconductive surface isselectively charged with a latent electrostatic image having image andbackground areas with different potentials. For example, anelectrostatic ink composition comprising charged toner particles in acarrier liquid can be brought into contact with the selectively chargedphotoconductive surface. The charged toner particles adhere to the imageareas of the latent image while the background areas remain clean. Theimage is then transferred to a print substrate (e.g. paper) directly or,more commonly, by being first transferred to an intermediate transfermember, which can be a soft swelling blanket, and then to the printsubstrate.

Many substrates are white, so the four main printing inks cyan, magenta,yellow and black (CMYK) are used, but for non-white substrates, whiteprinting inks are used.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1(a) shows the particle size distributions versus grinding time ofExamples 1 and 2 against a reference example;

FIG. 1(b) shows the percentage of particles having a particle diameterof greater than 20 microns versus grinding time of Examples 1 and 2against a reference example;

FIG. 2 shows optical density measurements of Examples 1 and 2 against areference example; and

FIG. 3 shows press test background and optical density results ofExample 2 against a reference example.

DETAILED DESCRIPTION

Before the present disclosure is disclosed and described, it is to beunderstood that this disclosure is not limited to the particular processsteps and materials disclosed herein because such process steps andmaterials may vary somewhat. It is also to be understood that theterminology used herein is used for the purpose of describing particularembodiments. The terms are not intended to be limiting because the scopeis intended to be limited by the appended claims and equivalentsthereof.

It is noted that, as used in this specification and the appended claims,the singular forms “a,” “an,” and “the” include plural referents unlessthe context clearly dictates otherwise.

As used herein, “carrier fluid”, “carrier liquid,” “carrier,” or“carrier vehicle” refers to the fluid in which pigment particles,colorant, charge directors and other additives can be dispersed to forma liquid electrostatic composition or electrophotographic composition.The carrier liquids may include a mixture of a variety of differentagents, such as surfactants, co-solvents, viscosity modifiers, and/orother possible ingredients.

As used herein, “electrostatic ink composition” or “liquidelectrophotographic composition” generally refers to an ink compositionthat is typically suitable for use in an electrostatic printing process,sometimes termed an electrophotographic printing process. It maycomprise pigment particles, which may comprise a thermoplastic resin.

As used herein, “co-polymer” refers to a polymer that is polymerizedfrom at least two monomers.

As used herein, “melt flow rate” generally refers to the extrusion rateof a resin through an orifice of defined dimensions at a specifiedtemperature and load, usually reported as temperature/load, e.g. 190°C./2.16 kg. Flow rates can be used to differentiate grades or provide ameasure of degradation of a material as a result of molding. In thepresent disclosure, “melt flow rate” is measured per ASTM D1238-04cStandard Test Method for Melt Flow Rates of Thermoplastics by ExtrusionPlastometer, as known in the art. If a melt flow rate of a particularpolymer is specified, unless otherwise stated, it is the melt flow ratefor that polymer alone, in the absence of any of the other components ofthe electrostatic composition.

As used herein, “acidity,” “acid number,” or “acid value” refers to themass of potassium hydroxide (KOH) in milligrams that neutralizes onegram of a substance. The acidity of a polymer can be measured accordingto standard techniques, for example as described in ASTM D1386. If theacidity of a particular polymer is specified, unless otherwise stated,it is the acidity for that polymer alone, in the absence of any of theother components of the liquid toner composition.

As used herein, “melt viscosity” generally refers to the ratio of shearstress to shear rate at a given shear stress or shear rate. Testing isgenerally performed using a capillary rheometer. A plastic charge isheated in the rheometer barrel and is forced through a die with aplunger. The plunger is pushed either by a constant force or at constantrate depending on the equipment. Measurements are taken once the systemhas reached steady-state operation. One method used is measuringBrookfield viscosity @ 140° C., units are mPa-s or cPoise, as known inthe art. Alternatively, the melt viscosity can be measured using arheometer, e.g. a commercially available AR-2000 Rheometer from ThermalAnalysis Instruments, using the geometry of: 25 mm steel plate-standardsteel parallel plate, and finding the plate over plate rheometryisotherm at 120° C., 0.01 hz shear rate. If the melt viscosity of aparticular polymer is specified, unless otherwise stated, it is the meltviscosity for that polymer alone, in the absence of any of the othercomponents of the electrostatic composition.

A certain monomer may be described herein as constituting a certainweight percentage of a polymer. This indicates that the repeating unitsformed from the said monomer in the polymer constitute said weightpercentage of the polymer.

If a standard test is mentioned herein, unless otherwise stated, theversion of the test to be referred to is the most recent at the time offiling this patent application.

As used herein, “electrostatic printing” or “electrophotographicprinting” generally refers to the process that provides an image that istransferred from a photo imaging substrate either directly or indirectlyvia an intermediate transfer member to a print substrate. As such, theimage is not substantially absorbed into the photo imaging substrate onwhich it is applied. Additionally, “electrophotographic printers” or“electrostatic printers” generally refer to those printers capable ofperforming electrophotographic printing or electrostatic printing, asdescribed above. “Liquid electrophotographic printing” is a specifictype of electrophotographic printing where a liquid composition isemployed in the electrophotographic process rather than a powder toner.An electrostatic printing process may involve subjecting theelectrostatic composition to an electric field, e.g. an electric fieldhaving a field gradient of 50-400V/μm, or more, ins some examples600-900V/μm, or more.

As used herein, “NVS” is an abbreviation of the term “non-volatilesolids”.

As used herein, the term “about” is used to provide flexibility to anumerical range endpoint by providing that a given value may be a littleabove or a little below the endpoint to allow for variation in testmethods or apparatus. The degree of flexibility of this term can bedictated by the particular variable and would be within the knowledge ofthose skilled in the art to determine based on experience and theassociated description herein.

As used herein, a plurality of items, structural elements, compositionalelements, and/or materials may be presented in a common list forconvenience. However, these lists should be construed as though eachmember of the list is individually identified as a separate and uniquemember. Thus, no individual member of such list should be construed as ade facto equivalent of any other member of the same list solely based ontheir presentation in a common group without indications to thecontrary.

Concentrations, amounts, and other numerical data may be expressed orpresented herein in a range format. It is to be understood that such arange format is used merely for convenience and brevity and thus shouldbe interpreted flexibly to include not just the numerical valuesexplicitly recited as the limits of the range, but also to include allthe individual numerical values or sub-ranges encompassed within thatrange as if each numerical value and sub-range is explicitly recited. Asan illustration, a numerical range of “about 1 wt % to about 5 wt %”should be interpreted to include not just the explicitly recited valuesof about 1 wt % to about 5 wt %, but also include individual values andsubranges within the indicated range. Thus, included in this numericalrange are individual values such as 2, 3.5, and 4 and sub-ranges such asfrom 1-3, from 2-4, and from 3-5, etc. This same principle applies toranges reciting a single numerical value. Furthermore, such aninterpretation should apply regardless of the breadth of the range orthe characteristics being described.

As used herein, wt % values are to be taken as referring to aweight-for-weight (w/w) percentage of solids in the ink composition, andnot including the weight of any carrier fluid present.

Unless otherwise stated, any feature described herein can be combinedwith any aspect or any other feature described herein.

In an aspect there is provided a method of producing a white liquidelectrophotographic ink composition, the method comprising:

-   -   heating a polymer resin in a carrier fluid to dissolve the        polymer resin;    -   suspending in the carrier fluid white pigment particles to be        coated; and    -   controlling cooling of the carrier fluid to effect precipitation        of the polymer resin from the carrier fluid such that a coating        of the resin is formed on the pigment particles, thereby        producing the white liquid electrophotographic ink composition.

In another aspect there is provided a white liquid electrophotographicink composition producible in accordance with a method comprising:

-   -   heating a polymer resin in a carrier fluid to dissolve the        polymer resin;    -   suspending in the carrier fluid white pigment particles to be        coated; and    -   controlling cooling of the carrier fluid to effect precipitation        of the polymer resin from the carrier fluid such that a coating        of the resin is formed on the pigment particles, thereby forming        the white liquid electrophotographic ink composition.

In another aspect there is provided a white liquid electrophotographicink composition, the composition comprising:

-   -   a carrier fluid; and    -   white pigment particles having a polymer resin coating thereon;        wherein the polymer resin coated white pigment particles have a        median particle size (d₅₀) of less than 20 μm after grinding for        45 minutes at 40° C., 250 rpm, and 18% non-volatile solids        content.

Much research has been carried out in recent years to try to create awhite electrostatic printing ink. Some electrostatic printing inks havebeen produced, e.g. by grinding a white pigment with a resin, sometimesin the presence of a liquid carrier. However, some of such inks havebeen found to have an insufficient and inconsistent white appearance,have a high level of background when printed, have increased tentacularshapes leading to increased ink concentration on the developer rollerand greater wetness on the roller and increased energy consumption,increased VOC emission and a decrease in T2 quality. The presentinventors have found that examples of the method as described hereinavoid or at least mitigate at least one of the difficulties describedabove. They have found that examples of the method are more successfulin encapsulating white pigment particles, and that the resulting pigmentparticles can be achieved via a more efficient and less energy intensiveproduction process.

Pigment

Although a variety of pigments may be used, in one example the pigmentis a white pigment particle. In some examples, the pigment particle maybe selected from the group consisting of TiO₂, calcium carbonate, zincoxide, and mixtures thereof, for example, the pigment may consistessentially of TiO₂. In some examples the pigment particle may be analumina-TiO₂ pigment. A form for the TiO₂ may be selected from amongrutile, anatase, brookite, and mixtures thereof, for example, the formmay consist of rutile. The rutile form of TiO₂ exhibits the highestrefractive index among the other forms of TiO₂ and the other listedpigments. All other parameters of inks being the same, the highestrefractive index yields the highest opacity. Examples of pigmentparticles include SACHTLEBEN® R405 from Sachtleben, and TI-PURE® R900from DuPont.

In some examples, the pigment particles are surface treated pigmentparticles. For example, the pigment particles may be organic surfacetreated or inorganic surface treated. In some examples, the pigmentparticles are surface treated to provide them with an increasedhydrophobicity. In some examples, the pigment particles are surfacetreated with a modified polysiloxane to provide increasedhydrophobicity.

In some examples, the pigment particles may have a median particle sizeor d₅₀ of less than 20 μm, for example less than 15 μm, for example lessthan 10 μm, for example less than 5 μm, for example less than 4 μm, forexample less than 3 μm, for example less than 2 μm, for example lessthan 1 μm, for example less than 0.9 μm, for example less than 08 μm,for example less than 0.7 μm, for example less than 0.6 μm, for exampleless than 0.5 μm. Unless otherwise stated, the particle size of thepigment particle and the coated pigment particle is determined usinglaser diffraction on a Malvern MASTERSIZER® 2000 according to thestandard procedure as described in the operating manual.

The pigment particle may be present in the method and/or electrostaticink composition in an amount of from 10 wt % to 80 wt % of the totalamount of resin and pigment, in some examples 15 wt % to 80 wt %, insome examples 15 wt % to 60 wt %, in some examples 15 wt % to 50 wt %,in some examples 15 wt % to 40 wt %, in some examples 15 wt % to 30 wt %of the total amount of resin and pigment. In some examples, the pigmentparticle may be present in the method and/or electrostatic inkcomposition in an amount of at least 50 wt % of the total amount ofresin and pigment, for example at least 55 wt % of the total amount ofresin and pigment.

Polymer Resin

The encapsulated particle can comprise a polymer resin. The polymerresin may comprise a thermoplastic polymer. A thermoplastic polymer issometimes referred to as a thermoplastic resin. In some examples, thepolymer may be selected from ethylene or propylene acrylic acidco-polymers; ethylene or propylene methacrylic acid co-polymers;ethylene vinyl acetate co-polymers; co-polymers of ethylene or propylene(e.g. 80 wt % to 99.9 wt %), and alkyl (e.g. C1 to C5) ester ofmethacrylic or acrylic acid (e.g. 0.1 wt % to 20 wt %); co-polymers ofethylene (e.g. 80 wt % to 99.9 wt %), acrylic or methacrylic acid (e.g.0.1 wt % to 20.0 wt %) and alkyl (e.g. C1 to C5) ester of methacrylic oracrylic acid (e.g. 0.1 wt % to 20 wt %); co-polymers of ethylene orpropylene (e.g. 70 wt % to 99.9 wt %) and maleic anhydride (e.g. 0.1 wt% to 30 wt %); polyethylene; polystyrene; isotactic polypropylene(crystalline); co-polymers of ethylene ethylene ethyl acrylate;polyesters; polyvinyl toluene; polyamides; styrene/butadieneco-polymers; epoxy resins; acrylic resins (e.g. co-polymer of acrylic ormethacrylic acid and at least one alkyl ester of acrylic or methacrylicacid wherein alkyl may have from 1 to about 20 carbon atoms, such asmethyl methacrylate (e.g. 50% to 90%)/methacrylic acid (e.g. 0 wt % to20 wt %)/ethylhexylacrylate (e.g. 10 wt % to 50 wt %));ethylene-acrylate terpolymers: ethylene-acrylic esters-maleic anhydride(MAH) or glycidyl methacrylate (GMA) terpolymers; ethylene-acrylic acidionomers and combinations thereof.

The resin may comprise a polymer having acidic side groups. Examples ofthe polymer having acidic side groups will now be described. The polymerhaving acidic side groups may have an acidity of 50 mg KOH/g or more, insome examples an acidity of 60 mg KOH/g or more, in some examples anacidity of 70 mg KOH/g or more, in some examples an acidity of 80 mgKOH/g or more, in some examples an acidity of 90 mg KOH/g or more, insome examples an acidity of 100 mg KOH/g or more, in some examples anacidity of 105 mg KOH/g or more, in some examples 110 mg KOH/g or more,in some examples 115 mg KOH/g or more. The polymer having acidic sidegroups may have an acidity of 200 mg KOH/g or less, in some examples 190mg or less, in some examples 180 mg or less, in some examples 130 mgKOH/g or less, in some examples 120 mg KOH/g or less. Acidity of apolymer, as measured in mg KOH/g can be measured using standardprocedures known in the art, for example using the procedure describedin ASTM D1386.

The resin may comprise a polymer, in some examples a polymer havingacidic side groups, that has a melt flow rate of less than about 70 g/10minutes, in some examples about 60 g/10 minutes or less, in someexamples about 50 g/10 minutes or less, in some examples about 40 g/10minutes or less, in some examples 30 g/10 minutes or less, in someexamples 20 g/10 minutes or less, in some examples 10 g/10 minutes orless. In some examples, all polymers having acidic side groups and/orester groups in the particles each individually have a melt flow rate ofless than 90 g/10 minutes, 80 g/10 minutes or less, in some examples 80g/10 minutes or less, in some examples 70 g/10 minutes or less, in someexamples 70 g/10 minutes or less, in some examples 60 g/10 minutes orless.

The polymer having acidic side groups can have a melt flow rate of about10 g/10 minutes to about 120 g/10 minutes, in some examples about 10g/10 minutes to about 70 g/10 minutes, in some examples about 10 g/10minutes to 40 g/10 minutes, in some examples 20 g/10 minutes to 30 g/10minutes. The polymer having acidic side groups can have a melt flow rateof, in some examples, about 50 g/10 minutes to about 120 g/10 minutes,in some examples 60 g/10 minutes to about 100 g/10 minutes. The meltflow rate can be measured using standard procedures known in the art,for example as described in ASTM D1238.

The acidic side groups may be in free acid form or may be in the form ofan anion and associated with one or more counterions, typically metalcounterions, e.g. a metal selected from the alkali metals, such aslithium, sodium and potassium, alkali earth metals, such as magnesium orcalcium, and transition metals, such as zinc. The polymer having acidicsides groups can be selected from resins such as co-polymers of ethyleneand an ethylenically unsaturated acid of either acrylic acid ormethacrylic acid; and ionomers thereof, such as methacrylic acid andethylene-acrylic or methacrylic acid co-polymers which are at leastpartially neutralized with metal ions (e.g. Zn, Na, Li) such as SURLYN®ionomers. The polymer comprising acidic side groups can be a co-polymerof ethylene and an ethylenically unsaturated acid of either acrylic ormethacrylic acid, where the ethylenically unsaturated acid of eitheracrylic or methacrylic acid constitute from 5 wt % to about 25 wt % ofthe co-polymer, in some examples from 10 wt % to about 20 wt % of theco-polymer.

The resin may comprise two different polymers having acidic side groups.The two polymers having acidic side groups may have different acidities,which may fall within the ranges mentioned above. The resin may comprisea first polymer having acidic side groups that has an acidity of from 10mg KOH/g to 110 mg KOH/g, in some examples 20 mg KOH/g to 110 mg KOH/g,in some examples 30 mg KOH/g to 110 mg KOH/g, in some examples 50 mgKOH/g to 110 mg KOH/g, and a second polymer having acidic side groupsthat has an acidity of 110 mg KOH/g to 130 mg KOH/g.

The resin may comprise two different polymers having acidic side groups:a first polymer having acidic side groups that has a melt flow rate ofabout 10 g/10 minutes to about 50 g/10 minutes and an acidity of from 10mg KOH/g to 110 mg KOH/g, in some examples 20 mg KOH/g to 110 mg KOH/g,in some examples 30 mg KOH/g to 110 mg KOH/g, in some examples 50 mgKOH/g to 110 mg KOH/g, and a second polymer having acidic side groupsthat has a melt flow rate of about 50 g/10 minutes to about 120 g/10minutes and an acidity of 110 mg KOH/g to 130 mg KOH/g. The first andsecond polymers may be absent of ester groups.

The ratio of the first polymer having acidic side groups to the secondpolymer having acidic side groups can be from about 10:1 to about 2:1.The ratio can be from about 6:1 to about 3:1, in some examples about4:1.

The resin may comprise a polymer having a melt viscosity of 15000 poiseor less, in some examples a melt viscosity of 10000 poise or less, insome examples 1000 poise or less, in some examples 100 poise or less, insome examples 50 poise or less, in some examples 10 poise or less; saidpolymer may be a polymer having acidic side groups as described herein.The resin may comprise a first polymer having a melt viscosity of 15000poise or more, in some examples 20000 poise or more, in some examples50000 poise or more, in some examples 70000 poise or more; and in someexamples, the resin may comprise a second polymer having a meltviscosity less than the first polymer, in some examples a melt viscosityof 15000 poise or less, in some examples a melt viscosity of 10000 poiseor less, in some examples 1000 poise or less, in some examples 100 poiseor less, in some examples 50 poise or less, in some examples 10 poise orless. The resin may comprise a first polymer having a melt viscosity ofmore than 60000 poise, in some examples from 60000 poise to 100000poise, in some examples from 65000 poise to 85000 poise; a secondpolymer having a melt viscosity of from 15000 poise to 40000 poise, insome examples 20000 poise to 30000 poise, and a third polymer having amelt viscosity of 15000 poise or less, in some examples a melt viscosityof 10000 poise or less, in some examples 1000 poise or less, in someexamples 100 poise or less, in some examples 50 poise or less, in someexamples 10 poise or less. An example of the first polymer is NUCREL®960 (from DuPont), and an example of the second polymer is NUCREL® 699(from DuPont), and an example of the third polymer is AC-5120 or AC-5180(from Honeywell). The first, second and third polymers may be polymershaving acidic side groups as described herein. The melt viscosity can bemeasured using a rheometer, e.g. a commercially available AR-2000Rheometer from Thermal Analysis Instruments, using the geometry of: 25mm steel plate-standard steel parallel plate, and finding the plate overplate rheometry isotherm at 120° C., 0.01 Hz shear rate.

If the resin comprises a single type of polymer, the polymer (excludingany other components of the electrophotographic ink composition) mayhave a melt viscosity of 6000 poise or more, in some examples a meltviscosity of 8000 poise or more, in some examples a melt viscosity of10000 poise or more, in some examples a melt viscosity of 12000 poise ormore. If the resin comprises a plurality of polymers all the polymers ofthe resin may together form a mixture (excluding any other components ofthe electrophotographic ink composition) that has a melt viscosity of6000 poise or more, in some examples a melt viscosity of 8000 poise ormore, in some examples a melt viscosity of 10000 poise or more, in someexamples a melt viscosity of 12000 poise or more. Melt viscosity can bemeasured using standard techniques. The melt viscosity can be measuredusing a rheometer, e.g. a commercially available AR-2000 Rheometer fromThermal Analysis Instruments, using the geometry of: 25 mm steelplate-standard steel parallel plate, and finding the plate over platerheometry isotherm at 120° C., 0.01 Hz shear rate.

The resin may comprise two different polymers having acidic side groupsthat are selected from co-polymers of ethylene and an ethylenicallyunsaturated acid of either acrylic acid or methacrylic acid; or ionomersthereof, such as methacrylic acid and ethylene-acrylic or methacrylicacid co-polymers which are at least partially neutralized with metalions (e.g. Zn, Na, Li) such as SURLYN® ionomers. The resin may comprise(i) a first polymer that is a co-polymer of ethylene and anethylenically unsaturated acid of either acrylic acid and methacrylicacid, wherein the ethylenically unsaturated acid of either acrylic ormethacrylic acid constitutes from 8 wt % to about 16 wt % of theco-polymer, in some examples 10 wt % to 16 wt % of the co-polymer; and(ii) a second polymer that is a co-polymer of ethylene and anethylenically unsaturated acid of either acrylic acid and methacrylicacid, wherein the ethylenically unsaturated acid of either acrylic ormethacrylic acid constitutes from 12 wt % to about 30 wt % of theco-polymer, in some examples from 14 wt % to about 20 wt % of theco-polymer, in some examples from 16 wt % to about 20 wt % of theco-polymer in some examples from 17 wt % to 19 wt % of the co-polymer.

The resin may comprise a polymer having acidic side groups, as describedabove (which may be free of ester side groups), and a polymer havingester side groups. The polymer having ester side groups may be athermoplastic polymer. The polymer having ester side groups may furthercomprise acidic side groups. The polymer having ester side groups may bea co-polymer of a monomer having ester side groups and a monomer havingacidic side groups. The polymer may be a co-polymer of a monomer havingester side groups, a monomer having acidic side groups, and a monomerabsent of any acidic and ester side groups. The monomer having esterside groups may be a monomer selected from esterified acrylic acid oresterified methacrylic acid. The monomer having acidic side groups maybe a monomer selected from acrylic or methacrylic acid. The monomerabsent of any acidic and ester side groups may be an alkylene monomer,including, but not limited to, ethylene or propylene. The esterifiedacrylic acid or esterified methacrylic acid may, respectively, be analkyl ester of acrylic acid or an alkyl ester of methacrylic acid. Thealkyl group in the alkyl ester of acrylic or methacrylic acid may be analkyl group having 1 to 30 carbons, in some examples 1 to 20 carbons, insome examples 1 to 10 carbons; in some examples selected from methyl,ethyl, iso-propyl, n-propyl, t-butyl, iso-butyl, n-butyl and pentyl.

The polymer having ester side groups may be a co-polymer of a firstmonomer having ester side groups, a second monomer having acidic sidegroups and a third monomer which is an alkylene monomer absent of anyacidic and ester side groups. The polymer having ester side groups maybe a co-polymer of (i) a first monomer having ester side groups selectedfrom esterified acrylic acid or esterified methacrylic acid, in someexamples an alkyl ester of acrylic or methacrylic acid, (ii) a secondmonomer having acidic side groups selected from acrylic or methacrylicacid and (iii) a third monomer which is an alkylene monomer selectedfrom ethylene and propylene. The first monomer may constitute 1% to 50%by weight of the co-polymer, in some examples 5% to 40% by weight, insome examples 5% to 20% by weight of the co-polymer, in some examples 5%to 15% by weight of the co-polymer. The second monomer may constitute 1%to 50% by weight of the co-polymer, in some examples 5% to 40% by weightof the co-polymer, in some examples 5% to 20% by weight of theco-polymer, in some examples 5% to 15% by weight of the co-polymer. Thefirst monomer can constitute 5% to 40% by weight of the co-polymer, thesecond monomer constitutes 5% to 40% by weight of the co-polymer, andwith the third monomer constituting the remaining weight of theco-polymer. In some examples, the first monomer constitutes 5% to 15% byweight of the co-polymer, the second monomer constitutes 5% to 15% byweight of the co-polymer, with the third monomer constituting theremaining weight of the co-polymer. In some examples, the first monomerconstitutes 8% to 12% by weight of the co-polymer, the second monomerconstitutes 8% to 12% by weight of the co-polymer, with the thirdmonomer constituting the remaining weight of the co-polymer. In someexamples, the first monomer constitutes about 10% by weight of theco-polymer, the second monomer constitutes about 10% by weight of theco-polymer, and with the third monomer constituting the remaining weightof the co-polymer. The polymer may be selected from the BYNEL® class ofmonomer, including BYNEL® 2022 and BYNEL® 2002, which are available fromDuPont.

The polymer having ester side groups may constitute 1% or more by weightof the total amount of the resin polymers, e.g. thermoplastic resinpolymers, in the liquid electrophotographic ink composition and/or theink printed on the print substrate, e.g. the total amount of the polymeror polymers having acidic side groups and polymer having ester sidegroups. The polymer having ester side groups may constitute 5% or moreby weight of the total amount of the resin polymers, e.g. thermoplasticresin polymers, in some examples 8% or more by weight of the totalamount of the resin polymers, e.g. thermoplastic resin polymers, in someexamples 10% or more by weight of the total amount of the resinpolymers, e.g. thermoplastic resin polymers, in some examples 15% ormore by weight of the total amount of the resin polymers, e.g.thermoplastic resin polymers, in some examples 20% or more by weight ofthe total amount of the resin polymers, e.g. thermoplastic resinpolymers, in some examples 25% or more by weight of the total amount ofthe resin polymers, e.g. thermoplastic resin polymers, in some examples30% or more by weight of the total amount of the resin polymers, e.g.thermoplastic resin polymers, in some examples 35% or more by weight ofthe total amount of the resin polymers, e.g. thermoplastic resinpolymers, in the liquid electrophotographic composition and/or the inkprinted on the print substrate. The polymer having ester side groups mayconstitute from 5% to 50% by weight of the total amount of the resinpolymers, e.g. thermoplastic resin polymers, in the liquidelectrophotographic composition and/or the ink printed on the printsubstrate, in some examples 10% to 40% by weight of the total amount ofthe resin polymers, e.g. thermoplastic resin polymers, in the liquidelectrophotographic composition and/or the ink composition printed onthe print substrate, in some examples 5% to 30% by weight of the totalamount of the resin polymers, e.g. thermoplastic resin polymers, in theliquid electrophotographic composition and/or the ink compositionprinted on the print substrate, in some examples 5% to 15% by weight ofthe total amount of the resin polymers, e.g. thermoplastic resinpolymers, in the liquid electrophotographic composition and/or the inkcomposition printed on the print substrate in some examples 15% to 30%by weight of the total amount of the resin polymers, e.g. thermoplasticresin polymers, in the liquid electrophotographic composition and/or theink composition printed on the print substrate.

The polymer having ester side groups may have an acidity of 50 mg KOH/gor more, in some examples an acidity of 60 mg KOH/g or more, in someexamples an acidity of 70 mg KOH/g or more, in some examples an acidityof 80 mg KOH/g or more. The polymer having ester side groups may have anacidity of 100 mg KOH/g or less, in some examples 90 mg KOH/g or less.The polymer having ester side groups may have an acidity of 60 mg KOH/gto 90 mg KOH/g, in some examples 70 mg KOH/g to 80 mg KOH/g.

The polymer having ester side groups may have a melt flow rate of about10 g/10 minutes to about 120 g/10 minutes, in some examples about 10g/10 minutes to about 50 g/10 minutes, in some examples about 20 g/10minutes to about 40 g/10 minutes, in some examples about 25 g/10 minutesto about 35 g/10 minutes.

The polymer, polymers, co-polymer or co-polymers of the resin can insome examples be selected from the NUCREL® family of toners (e.g.NUCREL® 403, NUCREL® 407, NUCREL® 609HS, NUCREL® 908HS, NUCREL® 1202HC,NUCREL® 30707, NUCREL® 1214, NUCREL® 903, NUCREL® 3990, NUCREL® 910,NUCREL® 925, NUCREL® 699, NUCREL® 599, NUCREL® 960, NUCREL® RX 76,NUCREL® 2806™, BYNEL® 2002, BYNEL® 2014, BYNEL® 2020 and BYNEL® 2022,(sold by DuPont)), the ACLYN® family of toners (e.g. ACLYN® 201, ACLYN®246, ACLYN® 285, and ACLYN® 295), and the LOTADER® family of toners(e.g. LOTADER® 2210, LOTADER®3430, and LOTADER® 8200 (sold by Arkema)).

The resin can constitute about 5 to 90%, in some examples about 50 to80%, by weight of the solids of the liquid electrophotographiccomposition and/or the ink composition printed on the print substrate.The resin can constitute about 60 to 95%, in some examples about 70 to95%, by weight of the solids of the liquid electrophotographiccomposition and/or the ink composition printed on the print substrate.

Carrier Liquid

In some examples, the composition comprises coated pigment particleswhich are formed in and/or dispersed in a carrier fluid or carrierliquid. Before application to the print substrate in the electrostaticprinting process, the composition may be an electrostatic inkcomposition, which may be in dry form, for example in the form offlowable pigment particles coated with the thermoplastic resin.Alternatively, before application to the print substrate in theelectrostatic printing process, the electrostatic ink composition may bein liquid form; and may comprise a carrier liquid in which is suspendedpigment particles coated with the thermoplastic resin.

Generally, the carrier liquid acts as a reaction solvent in preparingthe coated pigment particles, and can also act as a dispersing mediumfor the other components in the resulting electrostatic ink composition.In one example, the carrier liquid is a liquid which does not dissolvethe polymer resin at room temperature. In one example, the carrierliquid is a liquid which dissolves the polymer resin at elevatedtemperatures. For example, the polymer resin may be soluble in thecarrier liquid when heated to a temperature of at least 80° C., forexample 90° C., for example 100° C., for example 110° C., for example120° C. For example, the carrier liquid can comprise or be ahydrocarbon, silicone oil, vegetable oil, etc. The carrier liquid caninclude, but is not limited to, an insulating, non-polar, non-aqueousliquid that can be used as a medium for toner particles. The carrierliquid can include compounds that have a resistivity in excess of about10⁹ ohm-cm. The carrier liquid may have a dielectric constant belowabout 5, in some examples below about 3. The carrier liquid can include,but is not limited to, hydrocarbons. The hydrocarbon can include, but isnot limited to, an aliphatic hydrocarbon, an isomerized aliphatichydrocarbon, branched chain aliphatic hydrocarbons, aromatichydrocarbons, and combinations thereof. Examples of the carrier liquidsinclude, but are not limited to, aliphatic hydrocarbons, isoparaffiniccompounds, paraffinic compounds, dearomatized hydrocarbon compounds, andthe like. In particular, the carrier liquids can include, but are notlimited to, ISOPAR®-G, ISOPAR®-H, ISOPAR®-L, ISOPAR®-M, ISOPAR®-K,ISOPAR®-V, NORPAR® 12, NORPAR® 13, NORPAR® 15, EXXOL® D40, EXXOL® D80,EXXOL® D100, EXXOL® D130™, and EXXOL® D140™ (each sold by EXXONCORPORATION); TECLEN® N-16, TECLEN® N-20, TECLEN® N-22, NissekiNAPHTHESOL™ L, Nisseki NAPHTHESOL™ M, Nisseki NAPHTHESOL™ H, #0 SolventL™, #0 Solvent M™, #0 Solvent H™, Nisseki ISOSOL™ 300, Nisseki ISOSOL™400, AF-4™, AF-5™, AF-6™ and AF-7™ (each sold by NIPPON OILCORPORATION); IP SOLVENT™ 1620 and IP SOLVENT™ 2028 (each sold byIDEMITSU PETROCHEMICAL CO., LTD.); AMSCO™ OMS and AMSCO™ 460 (each soldby AMERICAN MINERAL SPIRITS CORP.); and ELECTRON™, POSITRON™, NEW™ II,PUROGEN™ HF (100% synthetic terpenes) (sold by ECOLINK™).

In the example in which the carrier liquid is acting as a solvent duringpreparation of the liquid electrophotographic ink composition comprisingcoated pigment particles, the carrier liquid can constitute about 20% to99.5% by weight of the composition, in some examples 50% to 99.5% byweight of the composition. In the example in which the carrier liquid isacting as a solvent during preparation of coated pigment particles, thecarrier liquid may constitute about 40 to 90% by weight of thecomposition. In the example in which the carrier liquid is acting as asolvent during preparation of coated pigment particles, the carrierliquid may constitute about 60% to 80% by weight of the composition. Inthe example in which the carrier liquid is acting as a solvent duringpreparation of coated pigment particles, the carrier liquid mayconstitute about 90% to 99.5% by weight of the composition, in someexamples 95% to 99% by weight of the composition.

Before printing, the carrier liquid can constitute about 20% to 99.5% byweight of the electrostatic ink composition, in some examples 50% to99.5% by weight of the electrostatic ink composition. Before printing,the carrier liquid may constitute about 40 to 90% by weight of theelectrostatic ink composition. Before printing, the carrier liquid mayconstitute about 60% to 80% by weight of the electrostatic inkcomposition. Before printing, the carrier liquid may constitute about90% to 99.5% by weight of the electrostatic ink composition, in someexamples 95% to 99% by weight of the electrostatic ink composition.

The ink, when printed on the print substrate, may be substantially freefrom carrier liquid. In an electrostatic printing process and/orafterwards, the carrier liquid may be removed, e.g. by anelectrophoresis processes during printing and/or evaporation, such thatsubstantially just solids are transferred to the print substrate.Substantially free from carrier liquid may indicate that the ink printedon the print substrate contains less than 5 wt % carrier liquid, in someexamples, less than 2 wt % carrier liquid, in some examples less than 1wt % carrier liquid, in some examples less than 0.5 wt % carrier liquid.In some examples, the ink printed on the print substrate is free fromcarrier liquid.

Charge Director and Charge Adjuvant

The liquid electrophotographic composition and/or the ink compositionprinted on the print substrate can comprise a charge director. A chargedirector can be added to an electrostatic composition to impart a chargeof a desired polarity and/or maintain sufficient electrostatic charge onthe particles of an electrostatic ink composition. The charge directormay comprise ionic compounds, including, but not limited to, metal saltsof fatty acids, metal salts of sulfo-succinates, metal salts ofoxyphosphates, metal salts of alkyl-benzenesulfonic acid, metal salts ofaromatic carboxylic acids or sulfonic acids, as well as zwitterionic andnon-ionic compounds, such as polyoxyethylated alkylamines, lecithin,polyvinylpyrrolidone, organic acid esters of polyvalent alcohols, etc.The charge director can be selected from, but is not limited to,oil-soluble petroleum sulfonates (e.g. neutral Calcium PETRONATE™,neutral Barium PETRONATE™, and basic Barium PETRONATE™), polybutylenesuccinimides (e.g. OLOA™ 1200 and Amoco AMOCO™ 575), and glyceride salts(e.g. sodium salts of phosphated mono- and diglycerides with unsaturatedand saturated acid substituents), sulfonic acid salts including, but notlimited to, barium, sodium, calcium, and aluminum salts of sulfonicacid. The sulfonic acids may include, but are not limited to, alkylsulfonic acids, aryl sulfonic acids, and sulfonic acids of alkylsuccinates (e.g. see WO 2007/130069). The charge director can impart anegative charge or a positive charge on the resin-containing particlesof an electrostatic ink composition.

The charge director can comprise a sulfosuccinate moiety of the generalformula

[R_(a)—O—C(O)CH₂CH(SO₃ ⁻)C(O)—O—R_(b)], where each of R_(a) and R_(b) isan alkyl group. In some examples, the charge director comprisesnanoparticles of a simple salt and a sulfosuccinate salt of the generalformula MA_(n), wherein M is a metal, n is the valence of M, and A is anion of the general formula [R_(a)—O—C(O)CH₂CH(SO₃ ⁻)C(O)—O—R_(b)], whereeach of R_(a) and R_(b) is an alkyl group, or other charge directors asfound in WO2007130069, which is incorporation herein by reference in itsentirety. As described in WO2007130069, the sulfosuccinate salt of thegeneral formula MA_(n) is an example of a micelle forming salt. Thecharge director may be substantially free or free of an acid of thegeneral formula HA, where A is as described above. The charge directormay comprise micelles of said sulfosuccinate salt enclosing at leastsome of the nanoparticles. The charge director may comprise at leastsome nanoparticles having a size of 200 nm or less, in some examples 2nm or more. As described in WO2007130069, simple salts are salts that donot form micelles by themselves, although they may form a core formicelles with a micelle forming salt. The ions constructing the simplesalts are all hydrophilic. The simple salt may comprise a cationselected from Mg, Ca, Ba, NH₄, tert-butyl ammonium, Li⁺, and Al⁺³, orfrom any sub-group thereof. The simple salt may comprise an anionselected from SO₄ ²⁻, PO³⁻, NO₃ ⁻, HPO₄ ²⁻, CO₃ ²⁻, acetate,trifluoroacetate (TFA), Cl⁻, Bf, F⁻, ClO₄ ⁻, and TiO₃ ⁴⁻, or from anysub-group thereof. The simple salt may be selected from CaCO₃, Ba₂TiO₃,Al₂(SO₄), Al(NO₃)₃, Ca₃(PO₄)₂, BaSO₄, BaHPO₄, Ba₂(PO₄)₃, CaSO₄,(NH₄)₂CO₃, (NH₄)₂SO₄, NH₄OAc, Tert-butyl ammonium bromide, NH₄NO₃,LiTFA, Al₂(SO₄)₃, LiClO₄ and LiBF₄, or any sub-group thereof. The chargedirector may further comprise basic barium petronate (BBP).

In the formula [R_(a)—O—C(O)CH₂CH(SO₃ ⁻)C(O)—O—R_(b)], in some examples,each of R_(a) and R_(b) is an aliphatic alkyl group. In some examples,each of R_(a) and R_(b) independently is a C₆₋₂₅ alkyl. In someexamples, said aliphatic alkyl group is linear. In some examples, saidaliphatic alkyl group is branched. In some examples, said aliphaticalkyl group includes a linear chain of more than 6 carbon atoms. In someexamples, R_(a) and R_(b) are the same. In some examples, at least oneof R_(a) and R_(b) is C₁₃H₂₇. In some examples, M is Na, K, Cs, Ca, orBa. The formula [R_(a)—O—C(O)CH₂CH(SO₃ ⁻)C(O)—O—R_(b)] and/or theformula MA_(n) may be as defined in any part of WO2007130069.

The charge director may comprise (i) soya lecithin, (ii) a bariumsulfonate salt, such as basic barium petronate (BPP), and (iii) anisopropyl amine sulfonate salt. Basic barium petronate is a bariumsulfonate salt of a 21-26 hydrocarbon alkyl, and can be obtained, forexample, from Chemtura. An example isopropyl amine sulphonate salt isdodecyl benzene sulfonic acid isopropyl amine, which is available fromCroda.

In an electrostatic ink composition, the charge director can constituteabout 0.001% to 20%, in some examples 0.01 to 20% by weight, in someexamples 0.01 to 10% by weight, in some examples 0.01 to 1% by weight ofthe solids of the electrostatic ink composition and/or ink compositionprinted on the print substrate. The charge director can constitute about0.001 to 0.15% by weight of the solids of the liquid electrophotographicink composition and/or ink composition printed on the print substrate,in some examples 0.001 to 0.15%, in some examples 0.001 to 0.02% byweight of the solids of the liquid electrophotographic ink compositionand/or ink composition printed on the print substrate. In some examples,the charge director imparts a negative charge on the electrostatic inkcomposition. The particle conductivity may range from 50 to 500 pmho/cm,in some examples from 200-350 pmho/cm.

The liquid electrophotographic ink composition and/or ink compositionprinted on the print substrate can include a charge adjuvant. A chargeadjuvant may be present with a charge director, and may be different tothe charge director, and act to increase and/or stabilise the charge onparticles, e.g. resin-containing particles, of an electrostaticcomposition. The charge adjuvant can include, but is not limited to,barium petronate, calcium petronate, Co salts of naphthenic acid, Casalts of naphthenic acid, Cu salts of naphthenic acid, Mn salts ofnaphthenic acid, Ni salts of naphthenic acid, Zn salts of naphthenicacid, Fe salts of naphthenic acid, Ba salts of stearic acid, Co salts ofstearic acid, Pb salts of stearic acid, Zn salts of stearic acid, Alsalts of stearic acid, Cu salts of stearic acid, Fe salts of stearicacid, metal carboxylates (e.g. Al tristearate, Al octanoate, Liheptanoate, Fe stearate, Fe distearate, Ba stearate, Cr stearate, Mgoctanoate, Ca stearate, Fe naphthenate, Zn naphthenate, Mn heptanoate,Zn heptanoate, Ba octanoate, Al octanoate, Co octanoate, Mn octanoate,and Zn octanoate), Co lineolates, Mn lineolates, Pb lineolates, Znlineolates, Ca oleates, Co oleates, Zn palmirate, Ca resinates, Coresinates, Mn resinates, Pb resinates, Zn resinates, AB diblockco-polymers of 2-ethylhexyl methacrylate-co-methacrylic acid calcium,and ammonium salts, co-polymers of an alkyl acrylamidoglycolate alkylether (e.g. methyl acrylamidoglycolate methyl ether-co-vinyl acetate),and hydroxy bis(3,5-di-tert-butyl salicylic) aluminate monohydrate. Insome examples, the charge adjuvant is aluminium di and/or tristearateand/or aluminium di and/or tripalmitate.

The charge adjuvant can constitute about 0.1 to 5% by weight of thesolids of the liquid electrophotographic ink composition and/or inkcomposition printed on the print substrate. The charge adjuvant canconstitute about 0.5 to 4% by weight of the solids of the liquidelectrophotographic ink composition and/or ink composition printed onthe print substrate. The charge adjuvant can constitute about 1 to 3% byweight of the solids of the liquid electrophotographic ink compositionand/or ink composition printed on the print substrate.

Other Additives

The electrophotographic ink composition may include an additive or aplurality of additives. The additive or plurality of additives may beadded at any stage of the method. The additive or plurality of additivesmay be selected from a wax, a surfactant, biocides, organic solvents,viscosity modifiers, materials for pH adjustment, sequestering agents,preservatives, compatibility additives, emulsifiers and the like. Thewax may be an incompatible wax. As used herein, “incompatible wax” mayrefer to a wax that is incompatible with the resin. Specifically, thewax phase separates from the resin phase upon the cooling of the resinfused mixture on a print substrate during and after the transfer of theink film to the print substrate, e.g. from an intermediate transfermember, which may be a heated blanket.

Method of Producing the Liquid Electrophotographic Ink Composition

In some examples, the method of producing a white liquidelectrophotographic ink composition involves heating a dispersion of apolymer resin in a carrier fluid to dissolve the polymer resin. In someexamples, the polymer resin is insoluble in the carrier fluid at roomtemperature but soluble in the carrier fluid at elevated temperatures,for example at a temperature of at least 50° C., for example at atemperature of at least 60° C., for example at a temperature of at least70° C., for example at a temperature of at least 80° C., for example ata temperature of at least 90° C., for example at a temperature of atleast 100° C., for example at a temperature of at least 110° C., forexample at a temperature of at least 120° C. The dispersion of thepolymer resin in the carrier fluid may be heated to any of the abovestated temperatures for sufficient time until the polymer resin hasdissolved. Dissolution may be confirmed by the carrier fluid appearingclear and homogenous. In some examples, the dispersion of polymer resinin the carrier fluid may be mixed at a rate of less than 500 rpm, forexample less than 400 rpm, for example less than 300 rpm, for exampleless than 200 rpm until dissolution is complete. In some examples,heating a dispersion of polymer resin in carrier fluid causes thepolymer resin to swell with carrier fluid. In some examples, thedispersion of polymer resin in carrier fluid is heated to swell thepolymer resin. Swelling of the polymer resin allows better encapsulationof the pigment particle.

In some examples, the white pigment particles may be suspended in thecarrier fluid before any cooling occurs, for example at the temperatureat which dissolution of the polymer resin in the carrier fluid wascarried out. In some examples, the carrier fluid may be cooled to anintermediate temperature before the pigment particles are suspended inthe carrier fluid. The intermediate temperature may be any temperatureabove the cloud point of the solution comprising the carrier fluid andthe dissolved polymer resin. The cloud point of any given carrierfluid-polymer resin system can be readily determined by heating andslowly cooling the solution and is the temperature at which dissolvedsolids begin to precipitate, giving a phase separation and a cloudy orturbid appearance. In some examples, the solution comprising the carrierfluid and the dissolved polymer resin is cooled to at least 2° C., forexample at least 3° C., for example at least 4° C., for example at least5° C., for example at least 6° C., for example at least 7° C., forexample at least 8° C., for example at least 9° C., for example at least10° C. above the cloud point before the pigment particle is suspended inthe carrier fluid.

In some examples, the pigment particles are mixed into the solution ofthe polymer resin dissolved in the carrier fluid at a shear rate of 12000 rpm or less, for example 11 000 rpm or less, for example 10 000 rpmor less, for example 9000 rpm or less to ensure complete dispersionbefore the precipitation of the polymer resin is effected. In otherexamples, the pigment particles are mixed into the solution of thepolymer resin dissolved in the carrier fluid at a shear rate of 100 rpmor less, for example 90 rpm or less, for example 80 rpm or less, forexample 70 rpm or less, for example 60 rpm or less, for example 50 rpmor less to ensure complete dispersion before the precipitation of thepolymer resin is effected. In some examples, following dispersion of thepigment particles at a low shear rate, the rate of mixing may beincreased to less than 100 rpm, for example less than 90 rpm, forexample less than 80 rpm, for example 70 rpm or less. In some examples,following dispersion of the pigment particles, the rate of mixing may belowered to less than 500 rpm, for example less than 400 rpm, for exampleless than 300 rpm, for example less than 200 rpm, for example 100 rpm orless, for example less than 90 rpm, for example less than 80 rpm, forexample less than 70 rpm, for example less than 60 rpm, for example 50rpm or less while precipitation is effected.

The precipitation is effected by controlling the cooling of the systemby any method such that solubility of the resin in the carrier fluid isreduced and precipitation of the resin occurs. In some examples, thetemperature of the carrier fluid is lowered through a controlled coolingprocess at a given rate. For example, after addition of the pigmentparticles, the temperature of the carrier fluid may be lowered at a rateof less than 5° C. per hour, for example less than 4° C. per hour, forexample less than 3° C. per hour, for example less than 2° C. per hour,for example less than 1° C. per hour.

In some examples, precipitation is effected through controlled coolingthrough the cloud point of the polymer resin-carrier fluid system. Forexample, the controlled cooling at a rate of less than 3° C./hour may becarried out beginning at a temperature of 5° C. above the cloud point ofthe solution and continued until a temperature of at least 5° C. belowthe cloud point of the solution. In some examples, once the temperaturehas been lowered in a controlled manner to at least 5° C. below thecloud point of the solution, the system is then cooled at anuncontrolled rate to room temperature.

In some examples, the effecting precipitation involves controllingcooling through addition of further carrier fluid at a controlled rate.For example, the further carrier fluid may be added at a rate of lessthan 10 cm³/min, for example less than 9 cm³/min, for example less than8 cm³/min, for example less than 7 cm³/min, for example less than 6cm³/min, for example less than 5 cm³/min, for example less than 4cm³/min, for example less than 3 cm³/min. In some examples, a sufficientamount of additional carrier fluid is added at a controlled rate inorder to effect phase separation, or effect precipitation. In someexamples, once precipitation is complete, the system is cooled at anuncontrolled rate to room temperature.

In some examples, following precipitation of the resin from the carrierfluid, the composition comprising polymer resin-coated pigment particlesin carrier fluid may be subjected to a grinding treatment. The grindingtreatment may comprise grinding the composition at a temperature of lessthan 100° C., for example less than 90° C., for example less than 80°C., for example less than 70° C., for example less than 60° C., forexample less than 50° C., for example 40° C. or less. The grindingtreatment may comprise grinding the composition at a speed of less than500 rpm, for example less than 400 rpm, for example less than 300 rpm,for example 250 rpm or less. The grinding treatment may comprisegrinding the composition at a NVS content of less than 40%, for exampleless than 30%, for example less than 20%, for example 18% or less. Thegrinding treatment may comprise grinding the composition for less than12 hours, for example less than 6 hours, for example less than 5 hours,for example less than 4 hours, for example less than 3 hours, forexample 2 hours or less. The grinding treatment may comprise grindingthe composition until a desired particle size is obtained.

In some examples, the composition resulting from the precipitation ofthe resin from the carrier fluid is suitable for use as or is convertedto an electrostatic ink composition, before or after the optionalgrinding step. The electrostatic ink composition may be a dry toner oran liquid toner composition. The electrostatic ink composition maycomprise coated particles comprising the resin and the pigmentparticles. In some examples, a particle comprises pigment particleshaving a coating of the resin thereon. In some examples, the coating ofresin on the pigment particles partially or completely encapsulates thepigment particles. In some examples, the electrostatic ink compositionmay comprise particles comprising the resin and the pigment particles,wherein at least some of the pigment particles are completelyencapsulated by the coating of the resin. In some examples, thecomposition resulting from the precipitation of the resin from theliquid carrier is suitable for use as or is converted to anelectrostatic ink composition by removing the liquid to leave dryparticles, comprising the resin and the coated pigment particles. Theparticles may be capable of developing a charge from the nature of theresin, e.g. if the resin has acidic side groups, to become chargeableparticles. In some examples, an electrostatic ink composition maycomprise a charge director. In some examples, a charge director may bepresent in the carrier liquid before precipitation of the resin. In someexamples, a charge director is added during or after precipitation ofthe resin. In some examples, a charge director is added to thecomposition resulting from the precipitation of the resin from theliquid carrier to convert it to an electrostatic ink composition.

In some examples, the pigment particles, excluding any coating thereon,constitute 25% or less by weight of the solids in the electrostatic inkcomposition or composition resulting from the method, which may be anelectrostatic ink composition. In some examples, the pigment particles,excluding any coating thereon, constitute 12% or less by weight, in someexamples 10% or less by weight, in some examples 8% or less by weight ofthe solids in the electrostatic ink composition or composition resultingfrom the method, which may be an electrostatic ink composition. In someexamples, the pigment particles, excluding any coating thereon,constitute 1% or more by weight, in some examples 2% or more by weight,in some examples 4% or more by weight, in some examples 6% or more byweight by weight, in some examples 8% or more by weight, of the solidsin electrostatic ink composition or composition resulting from themethod, which may be an electrostatic ink composition.

In some examples, the pigment particles, including any coating thereon,constitute 25% or less by weight of the solids in the electrostatic inkcomposition or composition resulting from the method, which may be anelectrostatic ink composition. In some examples, the pigment particles,including any coating thereon, constitute 12% or less by weight, in someexamples 10% or less by weight, in some examples 8% or less by weight ofthe solids in the electrostatic ink composition or composition resultingfrom the method, which may be an electrostatic ink composition. In someexamples, the pigment particles, including any coating thereon,constitute 1% or more by weight, in some examples 2% or more by weight,in some examples 4% or more by weight, in some examples 6% or more byweight by weight, in some examples 8% or more by weight, of the solidsin electrostatic ink composition or composition resulting from themethod, which may be an electrostatic ink composition.

The present disclosure further relates to a liquid electrophotographicink composition producible in accordance with a method described herein.

In some examples, the composition resulting from the precipitation ofthe resin from the liquid carrier is suitable for use as or is convertedto a liquid electrophotographic ink composition.

In some examples, the white liquid electrophotographic ink compositionmay be formed using a white pigment particle and a polymer resin aspreviously described. In one example, the white liquidelectrophotographic ink composition may comprise white pigment particlescoated with a polymer resin, wherein the polymer resin comprises acidicside groups as described previously. In one example, the white liquidelectrophotographic ink composition may comprise white pigment particlescoated with a polymer resin, wherein the polymer resin is or comprises apolymer having a melt flow rate as described previously.

In some examples, the white liquid electrophotographic ink compositionis produced directly from the methods described herein and is usable asa printing composition. In one example, the carrier fluid used in theresin precipitation process is or comprises the carrier fluid used forthe pigment resin coated particles in a printing process. Using in theprecipitation step a carrier fluid which is also useable as the carrierfluid in a printing process allows for a reduction in manufacturingcomplexity and thereby increases the efficiency of the process.

In one example, the polymer resin coated white pigment particles mayhave a median particle size (d₅₀) of less than 40 μm, for example lessthan 30 μm, less than 20 μm, less than 15 μm, less than 10 μm, less than9 μm, less than 8 μm, about 7 μm.

In one example, the white pigment particles having a polymer resincoating thereon may have a particular median particle size aftergrinding of the white liquid electrophotographic composition for a giventime under standard conditions. For example, the polymer resin coatedwhite pigment particles may have a median particle size of less than 20μm after grinding for 45 minutes at 40° C., 250 rpm, and 18%non-volatile solids content. Alternatively, the polymer resin coatedwhite pigment particles may have a median particle size of less than 8μm after grinding for 180 minutes at 40° C., 250 rpm, and 18%non-volatile solids content. Alternatively, the polymer resin coatedwhite pigment particles may have a median particle size of less than 7.5μm after grinding for 180 minutes at 40° C., 250 rpm, and 18%non-volatile solids content.

In one example, the polymer resin coated white pigment particles mayhave a percentage of particles having a size greater than 20 μm (“Tail20”) of less than 35%, for example less than 30%, less than 20%, lessthan 15%, less than 10%, less than 9%, less than 8%, less than 7%, lessthan 6%.

In one example, the white pigment particles having a polymer resincoating thereon may have a particular percentage of particles having asize greater than 20 μm (“Tail 20”) after grinding of the white liquidelectrophotographic composition for a given time under standardconditions. For example, the polymer resin coated white pigmentparticles may have a percentage of particles having a size greater than20 μm of less than 40% after grinding for 45 minutes at 40° C., 250 rpm,and 18% non-volatile solids content. Alternatively, the polymer resincoated white pigment particles may have a percentage of particles havinga size greater than 20 μm of less than 10% after grinding for 180minutes at 40° C., 250 rpm, and 18% non-volatile solids content.Alternatively, the polymer resin coated white pigment particles may havea percentage of particles having a size greater than 20 μm of less than7% after grinding for 180 minutes at 40° C., 250 rpm, and 18%non-volatile solids content.

The grinding may be carried out on any commercial attritor, for examplean S0, SD-1 or S1 attritor from Union Process. The grinding may becarried out using a metallic grinding media, or a non-metallic grindingmedia. The grinding media may be or comprise carbon steel, or chromesteel, or stainless steel, or steel shot. The grinding media may be orcomprise alumina or other ceramic material such as glass mullite siliconcarbide silicon nitride, tungsten carbide zirconium oxide, or zirconiumsilicate. The grinding media may be or comprise spherical orsubstantially spherical media, satellites or radius-end cylinders.Satellites will be understood as being substantially spherical with aprotruding band around the circumference. The grinding media may be 35mm or less in diameter, 31 mm or less in diameter, 30 mm or less indiameter, for example 26 mm or less, 25 mm or less, 15 mm or less, 12.7mm or less in diameter, 10 mm or less, for example 9.5 mm or less, 7.9mm or less, 5.6 mm or less, 6.4 mm or less, 3.9 mm or less, 3.2 mm orless, 2.4 mm or less, 2 mm or less, for example 1.7 mm or less, 1.4 mmor less, 1 mm or less, 1.18 mm or less, 0.7 mm or less, 0.6 mm or less,0.5 mm or less, 0.4 mm or less, or 0.25 mm or less in diameter.

The present disclosure also relates to a method of electrostaticprinting using an electrostatic ink composition as described herein,which may result from the method described herein, the electrostatic inkcomposition comprising resin-coated pigment particles, the methodcomprising:

-   -   forming a latent electrostatic image on a surface;    -   contacting the surface with the electrostatic ink composition,        such that at least some of the particles adhere to the surface        to form a developed toner image on the surface, and transferring        the toner image to a print substrate, in some examples, via an        intermediate transfer member.

The surface on which the latent electrostatic image is formed may be ona rotating member, e.g. in the form of a cylinder. The surface on whichthe latent electrostatic image is formed may form part of a photoimaging plate (PIP). The intermediate transfer member may be a rotatingflexible member, which may be heated, e.g. to a temperature of from 80to 130° C. The print substrate may be or comprise a cellulosic printsubstrate such as paper. The cellulosic print substrate may be orcomprise an uncoated cellulosic print substrate, i.e. absent of acoating of a polymeric material. The print substrate may be an acrylicprint substrate, in some examples a coated acrylic print substrate, e.g.coated with a styrene-butadiene co-polymer.

EXAMPLES

The following illustrates examples of the methods and related aspectsdescribed herein. Thus, these examples should not be considered aslimitations of the present disclosure, but are merely in place to teachhow to make examples of compositions of the present disclosure. As such,a representative number of compositions and their method of manufactureare disclosed herein.

Liquid Electrophotographic Ink Compositions

Materials

Resins: NUCREL® 599, NUCREL® 699 and NUCREL® 925 are allethylene-methacrylic acid copolymers available from DuPont. AC-5120 isan ethylene acrylic acid copolymer resin available from Honeywell.

Pigments: SACHTLEBEN® R405 pigment is available from Sachtleben, andTI-PURE® R900 is available from DuPont.

Solvent: ISOPAR®-L is available from Exxon-Mobil.

Example 1

A general procedure for coating pigment particles is described.

To prepare a 1 kg batch of coated particles, 200 g resin, 600 gISOPAR®-L and 200 g pigment were used.

Dispersed resin in carrier fluid (ISOPAR®-L) is heated to 100° C. andstirred at 200 rpm until fully dissolved and the solution is clear andhomogenous. At 100° C., pigment is added and mixed at a rate of 10 000rpm. An additional 200 g of ISOPAR®-L is then added at a rate of 5-10cc/min to dilute the solution.

The agitator speed is then reduced to 100 rpm in order not to interruptthe precipitation process. Once phase separation is complete, thedisperser is turned off and cooled to room temperature at the maximumcooling rate.

The above process results in approximately 1 kg of ink composition whichmay be used as or converted to a liquid electrophotographic printingcomposition at 20% NVS.

The resultant composition is then subjected to a grinding step at 40°C., 250 rpm, 1700 g at 18% NVS for up to 3 hours in an SD-1 laboratoryattritor from Union Process, with samples taken at various time points.

Example 2

An alternative process for preparing coating particles is described.

To prepare a 1 kg batch of coated particles, 200 g resin, 600 gISOPAR®-L and 200 g pigment were used.

The coating procedure takes place in a Kinematica REACTRON® RT2 sealedvessel with anchor mixing blades with scrapers which wipe the surface ofthe vertical cylindrical vessel wall to create good circulation of thematerial to be dissolved or dispersed and minimized temperaturedifferential between the wall and the bulk due to disruption of theviscous boundary layer at the wall. It is equipped with a heating jacketto allow the process to be carried out under controlled conditions oftemperature programming.

Dispersed resin in carrier fluid (ISOPAR®-L) is heated to 100° C. andstirred at 200 rpm until fully dissolved and the solution is clear andhomogenous. At this point the solution is above the cloud point andcooling can begin.

The solution is then cooled without restriction till the temperature is75° C., corresponding to 5° C. above the cloud point of the system. Thepigment is then added and mixed at a high shear rate of 10 000 rpm.

The agitator speed is then reduced to 100 rpm in order not to interruptthe precipitation process and the solution is then very slowly cooled ata rate of between 2-3° C./hr till phase separation has occurred andprecipitation of the polymer resin.

The above process results in approximately 1 kg of ink composition whichmay be used as or converted to a liquid electrophotographic printingcomposition at 40% NVS.

The resultant composition is then subjected to a grinding step at 40°C., 250 rpm, 1700 g at 18% NVS for up to 3 hours in an SD-1 laboratoryattritor from Union Process with samples taken at various time points.

Results

The median particle sizes (d₅₀; FIG. 1(a)) and percentage of particleshaving a particle diameter of greater than 20 microns (Tail 20%; FIG.1(a)) of Examples 1 and 2 as a function of grinding time are shown inFIGS. 1(a) and 1(b), respectively, together with a reference ink formedby grinding without the encapsulation/precipitation step. As can beseen, the coated pigment particles formed by precipitation have a muchsmaller particle size distribution than the reference particles, meaningthat less grinding is required to produce a coated pigment particle of agiven size. A shorter grinding procedure represents an improvedefficiency in the production process.

Optical density measurements on a 939 0°/45° portablespectrodensitometer from Xrite show that the reduction in grinding timeas a result of the encapsulation via precipitation has no adverse effecton the optical density of these pigments (FIG. 2). The optical densitymeasurements for Examples 1 and 2 were taken after 3 hours of grindingas described above, whereas the measurement for the reference examplewas taken after 5 hours of grinding. Furthermore, printing twoseparations of a precipitated ink formulation on a HP WS6000 DigitalPress showed that the precipitated ink composition according to Example2 has lower background levels and the ability to reach lower opticaldensities within a wider operational window when compared to a referenceink prepared by grinding (FIG. 3).

While the compositions, methods and related aspects have been describedwith reference to certain examples, those skilled in the art willappreciate that various modifications, changes, omissions, andsubstitutions can be made without departing from the spirit of thedisclosure. It is intended, therefore, that the invention be limited bythe scope of the following claims. The features of any dependent claimmay be combined with the features of any of the other dependent claimsor any and/or any of the independent claims.

The invention claimed is:
 1. A method of producing a white liquidelectrophotographic ink composition, the method comprising: heating apolymer resin in a carrier fluid to dissolve the polymer resin;suspending in the carrier fluid white pigment particles to be coated;and controlling cooling of the carrier fluid to effect precipitation ofthe polymer resin from the carrier fluid such that a coating of theresin is formed on the pigment particles, thereby producing the whiteliquid electrophotographic ink composition, wherein the precipitation iseffected by controlled addition of extra carrier fluid at a rate of lessthan 10 cm³/min.
 2. The method according to claim 1, wherein the carrierfluid is or comprises an isoparaffinic carrier fluid.
 3. The methodaccording to claim 1, wherein the carrier fluid is heated to at least100° C. to dissolve the polymer resin.
 4. The method according to claim1, further comprising grinding the polymer resin coated white pigmentparticles.
 5. The method according to claim 4 wherein: the white liquidelectrophotographic ink composition has 18% non-volatile solids content;and the grinding is accomplished at 40° C. and 250 rpm for up to 3hours.
 6. The method according to claim 5 wherein the grinding isaccomplished for 45 minutes.
 7. The method according to claim 5 whereinthe polymer resin coated white pigment particles have a median particlesize (d₅₀) of less than 20 μm after the grinding.
 8. The methodaccording to claim 1, further comprising adding a charge director: tothe carrier liquid before precipitation of the polymer resin; or to thecarrier liquid during precipitation of the polymer resin; or to thecarrier liquid after precipitation of the polymer resin.
 9. The methodaccording to claim 1 wherein the white pigment particle comprisessurface modifying groups to increase hydrophobicity.
 10. The methodaccording to claim 1 wherein the white pigment particles are selectedfrom the group consisting of TiO₂, calcium carbonate, zinc oxide, andmixtures thereof.
 11. A method of producing a white liquidelectrophotographic ink composition, the method comprising: heating apolymer resin in a carrier fluid to dissolve the polymer resin;suspending in the carrier fluid white pigment particles to be coated;and controlling cooling of the carrier fluid to effect precipitation ofthe polymer resin from the carrier fluid such that a coating of theresin is formed on the pigment particles, thereby producing the whiteliquid electrophotographic ink composition, wherein precipitation iseffected by cooling the carrier fluid containing dissolved polymer resinand suspended pigment particles at a rate of less than 5° C. per hour.12. The method according to claim 11, wherein the precipitation iseffected by cooling the carrier fluid containing dissolved polymer resinand suspended pigment particles at a rate of less than 3° C. per hour.